text: Ceramic microstructures are most often analyzed by reflected visible-light microscopy in brightfield.  Darkfield is used in limited circumstances, e.g., to reveal cracks.  Polarized transmitted light is used with thin sections, where the contrast between grains comes from birefringence. Very fine microstructures may require the higher magnification and resolution of a scanning electron microscope (SEM) or confocal laser scanning microscope (CLSM).  The cathodoluminescence microscope (CLM) is useful for distinguishing phases of refractories.  The transmission electron microscope (TEM) and scanning acoustic microscope (SAM) have specialty applications in ceramography.
  Ceramography is often done qualitatively, for comparison of the microstructure of a component to a standard for quality control or failure analysis purposes.  Three common quantitative analyses of microstructures are grain size, second-phase content and porosity.  Microstructures are measured by the principles of stereology, in which three-dimensional objects are evaluated in 2-D by projections or cross-sections. Microstructures exhibiting heterogeneous grain sizes, with certain grains growing very large, occur in diverse ceramic systems and this phenomenon is known as abnormal grain growth or AGG. The occurrence of AGG has consequences, positive or negative, on mechanical and chemical properties of ceramics and its identification is often the goal of ceramographic analysis. 
  Grain size can be measured by the line-fraction or area-fraction methods of ASTM E112.  In the line-fraction methods, a statistical grain size is calculated from the number of grains or grain boundaries intersecting a line of known length or circle of known circumference.  In the area-fraction method, the grain size is calculated from the number of grains inside a known area.  In each case, the measurement is affected by secondary phases, porosity, preferred orientation, exponential distribution of sizes, and non-equiaxed grains.  Image analysis can measure the shape factors of individual grains by ASTM E1382.
  Second-phase content and porosity are measured the same way in a microstructure, such as ASTM E562.  Procedure E562 is a point-fraction method based on the stereological principle of point fraction = volume fraction, i.e., P = V.  Second-phase content in ceramics, such as carbide whiskers in an oxide matrix, is usually expressed as a mass fraction.  Volume fractions can be converted to mass fractions if the density of each phase is known.  Image analysis can measure porosity, pore-size distribution and volume fractions of secondary phases by ASTM E1245.  Porosity measurements do not require etching.  Multi-phase microstructures do not require etching if the contrast between phases is adequate, as is usually the case.
  Grain size, porosity and second-phase content have all been correlated with ceramic properties such as mechanical strength σ by the Hall–Petch equation. Hardness, toughness, dielectric constant and many other properties are microstructure-dependent.